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\begin{document}
It's really true that:
\begin{itemize}
  \item The first item is always before the second item.
  \item The reasons for this are:
  \begin{itemize}
    \item mathematicians tell us so, and
    \item common sense tells us so.
  \end{itemize}
  \item Nonsense should not always be omitted.
\end{itemize}
 
The \LaTeX\ user needs:
\begin{enumerate}
  \item   a \LaTeX\ book --- there are several good books.
       For German users we recommend H.~Kopka's books.
  \item   a computer.
\end{enumerate}
The \LaTeX\ user needs very little beyond this.

The \LaTeX\ user needs:
\begin{description}
  \item[a \LaTeX\ book:]
      {in general a blue book, several of which are quite good. \par
       For German users we recommend H.~Kopka's books.
      }
  \item[a Computer:] {a black box}
\end{description}
The \LaTeX\ user needs very little beyond this.
\end{document}
